Projectors for projecting images are used to keep the unavoidable background brightness as low as possible, which leads to a better representation of black image contents (with zero brightness). However, the difficulty arises that, in the case of dark image contents, the lowest input grey shades (i.e. the grey-scale values which are adjacent to the grey-scale value=zero=black) can no longer be represented so as to be distinguishable from the remaining background brightness in the projected image. So-called temporal dithering and/or spatial dithering is often resorted to here. In the case of temporal dithering, the grey-scale value to be represented is only represented correctly averaged over several successively projected images (or single images or frames) which are in each case generated for a predetermined frame duration. This means that, for example in the case of five successive frames, the corresponding pixel is only switched on in two or three frames and is switched off in the other frames. Averaged over the five frames, the desired grey-scale value can then be reasonably well represented. In the case of spatial or local dithering, the averaging is carried out over the switching on and off of adjacent pixels in a single frame. With such dithering, on the one hand not all grey-scale values can be represented. Especially the grey-scale values which are adjacent to the grey-scale value zero cannot be represented in this way. On the other hand, the dithering generates flickering which many viewers perceive as annoying. It is furthermore possible to combine local and temporal dithering and to vary them over successive frames in order to conceal the “dither pattern”—however this also leads to flickering.
These difficulties in particular also result in a poorer image impression if several projectors are used to project a large overall image, wherein in this case the projected images are projected overlapping in the edge area in order to provide a continuous image impression. If such a low grey-scale value is to be represented in this edge area, this leads to even higher brightnesses in the case of low input brightnesses because of the brightness represented at too high a level by each of the two projectors.